This application is based on Japanese Patent Application No. 10-233921, filed Aug. 20, 1998, the contents of which are incorporated herein by reference.
The present invention relates to an encryption/decryption apparatus and method and, more particularly, to an encryption/decryption apparatus and method which use secret key block encryption and a program storage medium therefor.
The DES (Data Encryption Standard) is secret key block cipher that has currently been used most widely, which is described in detail in Jpn. Pat. Appln. KOKAI Publication No. 51-108701.
The DES has been evaluated in various viewpoints, and cryptanalysis such as a differential cryptanalysis and linear cryptanalysis, which are more effective than a key exhaustive search method, have been proposed.
Note that the differential cryptanalysis is disclosed in E. Biham and A. Shamir, “Differential Cryptanalysis of DES-like Cryptosystems,” Journal of CRYPTOLOGY, Vol. 4, Number 1, 1991. The linear decryption method is disclosed in Mitsuru Matsui, “Linear Cryptanalysis of DES Cipher”, Encryption and Information Security Symposium, SCIS93-3C, 1993.
There is a new cryptanalysis based on power consumption differences. In this method, power consumption differences between given bits of data (power consumption corresponding to bit 0 and power consumption corresponding to bit 1) are measured to estimate bits. In the case of the DES, for example, an input to an S-box and a corresponding output are estimated on the basis of a known ciphertext output and estimation of a key. A power consumption difference that appears when a given one bit is 0 or 1, which is estimated on the basis of the output from the S-box, is measured to check the validity of estimation, i.e., the validity of estimation of the key.
For this reason, there is a possibility that a DES ciphertext is broken by the above method, and hence higher security has been required.